1. Field of the Invention
The present invention relates to a method of making a diamond product by etching, and the diamond product.
2. Related Background Art
Plasma etching, which can remove a large amount of diamond at once and can be carried out relatively easily, has been utilized as a technique for processing diamond. Usually, oxygen gas is used for plasma etching of diamond. Etching with oxygen alone, however, has formed a large number of unnecessary acicular protrusions on the surface of the resulting diamond product, thus failing to smooth the surface. Therefore, attention has been given to a technique in which other gases are introduced into a reaction chamber together with oxygen gas so as to flatten the diamond surface. For example, Hiroshi Shiomi, New Diamond, Vol. 13, No. 4, p. 28 (1997) discloses a technique in which diamond is etched with a plasma of a mixed gas composed of oxygen gas and CF4 gas. This etching technique enables the plasma of CF4 gas to remove the unnecessary acicular protrusions and flatten the surface of diamond product.
However, the technique disclosed in the above-mentioned publication has the following problem. Namely, when a diamond substrate 102 is etched by way of a mask 104 as shown in FIG. 14A, thus etched side faces 102S may not become perpendicular but tilt greatly as shown in FIG. 14B, thus yielding a trapezoidal cross section.
In order to overcome the above-mentioned problem, it is an object of the present invention to provide a method of making a diamond product, which can fully flatten the surface of diamond product and make its etched side faces substantially perpendicular; and such a diamond product.
The inventors carried out diligent studies and, as a result, have found that the above-mentioned object can be achieved by the following invention.
Namely, the present invention provides a method of making a diamond product by etching, the method comprising the steps of forming a diamond substrate with a mask layer; and etching the diamond substrate formed with the mask layer with a plasma of a mixed gas composed of a gas containing an oxygen atom and a gas containing a fluorine atom; wherein the fluorine atom has a concentration within the range of 0.04% to 6% with respect to the total number of atoms in the mixed gas.
The inventors have found that, though the unnecessary protrusions can be eliminated when the fluorine concentration in the etching gas is raised, the mask layer is laterally shaved with fluorine when its concentration is too high, so that the etched side faces may incline. In recognition of this fact, the inventors have found that, when the fluorine atom concentration is lowered so as to fall within the above-mentioned range, the mask layer is restrained from being shaved laterally, whereby the etched side faces can be made substantially perpendicular; and that, even when the fluorine atom concentration is lowered so as to fall within the above-mentioned range, the number of unnecessary protrusions is sufficiently reduced, whereby the etched surface of diamond product is flattened.
Preferably, in the method of making a diamond product in accordance with the present invention, the plasma is produced by generating a high-frequency discharge between two plate electrodes arranged in parallel, whereas the high-frequency discharge is generated by supplying an electric power of at least 0.45 W/cm2 between the plate electrodes.
When the output for generating the high-frequency discharge is enhanced as such, it becomes easier for the fluorine atom to attain a plasma state, whereby the number of unnecessary protrusions can sufficiently be reduced even when the amount of fluorine is small.
Preferably, in the method of making a diamond product in accordance with the present invention, the gas containing the fluorine atom is CF4 gas, whereas the CF4 gas has a concentration within the range of 0.02% to 3% with respect to the total number of molecules in the mixed gas.
When CF4 gas, which is safe and easy to use, is employed, an etching process for the diamond substrate can be carried out smoothly.
Preferably, in the method of making a diamond product in accordance with the present invention, the gas containing the oxygen atom is one of O2, CO2, and a mixed gas composed of O2 and CO2.
The diamond product in accordance with one aspect of the present invention comprises a diamond substrate; a plurality of aligned protrusions made of diamond, formed on the diamond substrate by etching, and arranged according to a predetermined rule; and a plurality of subsidiary protrusions randomly formed between the plurality of aligned protrusions upon etching; wherein the aligned protrusions have a side face with an angle of inclination of at least 78xc2x0, whereas the subsidiary protrusions have a top part which is not flat, and the number of the subsidiary protrusions is not greater than 20 per 25 xcexcm2.
Among diamond products in which a plurality of protrusions are formed by etching, those having such a small number of subsidiary protrusions with their aligned protrusions having side faces with an angle of inclination of at least 78xc2x0 have not conventionally existed. For example, the above-mentioned manufacturing method of the present invention can make a diamond product having a flat surface with aligned protrusions having substantially perpendicular side faces as such. The portion of diamond substrate covered with the mask layer can attain a flat top part when the mask layer is removed. However, the subsidiary protrusions are formed in a portion not covered with the mask, whereby their top part is not flat. Here, the condition that the number of the subsidiary protrusions is not greater than 20 per 25 xcexcm2 also encompasses the case where there is no subsidiary protrusion.
The diamond product in accordance with another aspect of the present invention comprises a diamond substrate having a recess formed by etching; and a plurality of subsidiary protrusions randomly formed at a bottom part of the recess upon etching; wherein the recess has a side face with an angle of inclination of at least 78xc2x0, whereas the subsidiary protrusions have a top part which is not flat, and the number of the subsidiary protrusions is not greater than 20 per 25 xcexcm2.
Among diamond products in which a recess is formed by etching, those having such a small number of subsidiary protrusions with their recess having a side face with an angle of inclination of at least 78xc2x0 have not conventionally existed. The above-mentioned manufacturing method of the present invention can make a diamond product having a flat surface (bottom part of the recess) with the recess having a substantially perpendicular side face as such. Here, the condition that the number of the subsidiary protrusions is not greater than 20 per 25 xcexcm2 also encompasses the case where there is no subsidiary protrusion.
The diamond product in accordance with another aspect of the present invention comprises a diamond substrate; one protrusion made of diamond and formed on the diamond substrate by etching; and a plurality of subsidiary protrusions randomly formed about the one protrusion upon etching; wherein the one protrusion has a side face with an angle of inclination of at least 78xc2x0, whereas the subsidiary protrusions have a top part which is not flat, and the number of the subsidiary protrusions is not greater than 20 per 25 xcexcm2.
Among diamond products in which one protrusion is formed by etching, those having such a small number of subsidiary protrusions with the one protrusion having a side face with an angle of inclination of at least 78xc2x0 have not conventionally existed. The above-mentioned manufacturing method of the present invention can make a diamond product having a flat surface with the one protrusion having substantially perpendicular side faces as such. The portion of diamond substrate covered with the mask layer can attain a flat top part when the mask layer is removed. However, the subsidiary protrusions are formed in a portion not covered with the mask, whereby their top part is not flat. Here, the condition that the number of the subsidiary protrusions is not greater than 20 per 25 xcexcm2 also encompasses the case where there is no subsidiary protrusion.
The method of making a diamond product in accordance with another aspect of the present invention is a method of making a diamond product by etching, the method comprising the steps of forming a diamond substrate with a mask layer; and etching the diamond substrate formed with the mask layer with a plasma of a mixed gas composed of a gas containing an oxygen atom and a gas containing a halogen atom; wherein, in an emission spectrum of the mixed gas, an intensity A of an emission peak caused by the oxygen atom and an intensity B of an emission peak caused by oxygen have an intensity ratio A/B which is greater than the intensity ratio A/B obtained from an emission of a plasma which is 100% oxygen.
The greater the intensity ratio A/B is, the greater becomes the ratio of oxygen atom (O) to oxygen (O2). The oxygen atom is easier to etch diamond than is the oxygen molecule, thus improving the etching speed. Also, the mask layer is formed with a firm oxide film as the oxygen atom concentration increases. Therefore, the mask layer is restrained from being shaved laterally, whereby the etched side faces can be made substantially perpendicular. Further, the halogen atom can remove the unnecessary protrusions formed upon etching.
Preferably, the gas containing the halogen atom in the above-mentioned mixed gas is CF4, and the mixed gas further contains nitrogen gas. The inventors have found that, when the mixed gas is composed as such, the intensity ratio A/B improves, thereby enhancing the diamond etching speed.
Also, the emission peak caused by the oxygen atom may have a half width of 3 nm or less, whereas the emission peak caused by oxygen may have a half width greater than 3 nm.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.